The research aims to investigate the generation and distribution of the residual stress in diamond thin films and explore methods of relieving it. Firstly, the finite element analysis software ANSYS Workbench was used to simulate the thermal stress of diamond thin films during the cooling process, and the effect of film thickness on thermal stress was studied. Then through the microwave plasma chemical vapor deposition (MPCVD), diamond thin films of varying thicknesses were deposited on aluminum nitride (AlN) ceramics substrates. The cooling duration was manipulated and annealing treatments were conducted. Characterization analyses were finally carried out using SEM and Raman spectroscopy. The simulation shows that after the cooling process, the distribution of thermal stress is irregular, with the maximum principal stress being tensile stress and the minimum principal stress being compressive stress. As the thickness of diamond thin films increases, the maximum principal stress shows an ascending trend, reaching a peak value of 373 MPa when the film thickness is 200 μm, which is close to the normal fracture strength range of diamond thin films (400 ～ 700 MPa). Conversely, the minimum principal stress and shear stress exhibit a decline as the film thickness increases. Raman characterization indicates that the surface of the diamond thin films has residual compressive stress. This residual stress decreases with increasing film thickness and cooling duration. After in-situ annealing at 600 ℃ in a hydrogen atmosphere, the stress-induced distortion in the films is alleviated, and there is a noticeable enhancement in the intensity of the diamond phase Raman peak.